DESCRIPTION (Investigator's abstract): Using magnetoencephalographic recordings we have repeatedly demonstrated that the late positive component of event related potentials (P3) is most likely generated by two clusters of sources. One cluster, common to all types of P3s we have recorded, involves the thalamus and/or the hippocampus. The other cluster is found in the sensory cortex specific to each stimulus modality. There appears to be no difference in the source configuration of P3s to missing and to odd-ball stimuli. This finding, along with the fact that P3s to frequent stimuli-in addition to rare and unpredictable ones- also appear in the MEG records, suggests that P3s may be indicative of mere changes in the subject's psychological state and not necessarily of the nature of the state (i.e., the type of cognitive operations occasioned by the stimulus or the significance of the stimulus). On the other hand, the sources of magnetically recorded Contingent Negative Variation (CNV) do vary according to task demands, ranging over different parts of the frontal lobes depending on the nature of the cognitive operations in which the subjects are preparing to engage. In this project, we aim to record both P3s and CNVs in the context of the same tasks and characterize their sources in an attempt to discover what aspects of the cognitive operations required by these tasks are reflected by each. In this way, in addition to identifying the sources of P3s and CNVs, we expect to advance understanding of the specialization of the frontal lobes and their functional connections with archeocortical structures and the sensory cortex in mediating complex cognitive operations.